Amnesty said more than 300,000 people are detained by US immigration officials each year, including asylum seekers, torture survivors, victims of human trafficking, legal permanent residents and the parents of US citizens.

"The use of detention as a tool to combat unauthorised migration falls short of international human rights law," the report said.

Representation difficult

The US Department of Homeland Security has the power to detain people at the border or during raids if it suspects them of an immigration violation.

People detained at the border are not entitled to a review of their detention by an immigration judge, Amnesty said.

Those apprehended inside the US have the right to appear before a judge, but the wait can be long.

The report also said that it is so difficult for most detainees to get legal representation that many ask to be deported from the US even if they believe they are entitled to stay.

The Amnesty report said US citizens were also incorrectly subjected to detention with no right to a hearing before a judge and spent months or years behind bars before proving they could not be deported.

According to the report, there were about 12 million illegal immigrants living in the US as of January 2007.

The top five countries of origin were Mexico, El Salvador, Guatemala, the Philippines and China.